The present invention relates to a data allocation method applicable to a data storage apparatus equipped with a single or a plurality of rotary recording surfaces and heads for writing and reading data into and from the recording surfaces, also to a recording medium with data stored by the method, and to a data server apparatus for reading data stored in the data storage apparatus and transferring the read data to a terminal where a request for reading the data has issued.
Data recording apparatus includes magnetic tapes, magnetic disks, optical magnetic disks, etc. Magnetic disks, which are randomly accessible devices are advantageous in that they can be accessed at a higher speed than magnetic tapes, although the former are more expensive and have a smaller storage capacity than the latter.
The magnetic disk which has formally had a smaller storage capacity is advanced to have a larger storage capacity with low price by the development of recent technology, thereby its cost performance is improved to a grade in which a large amount of data in the form of, for example, moving picture can be stored. In addition, to the increase of the disk capacity, the band width of the network has been improved. These circumstances have enabled new services such as "video on demand"
Taking the "video on demand" service as an example, the operation of a data recording apparatus and a data allocation method employed therein will be explained.
In a service, such as the "video on demand", for distributing large amount of data of plural types to large number of users, data stored in data recording apparatuses like magnetic disks must be read at high speed within a predetermined time period. The rotary type data recording apparatus includes a magnetic disk, a magneto-optical disk (MO), or an optical disk, for example. In general, in a rotary type data recording apparatus, during a reading or writing process, a seek operation of moving the head to the target sector of the recording surface which records data to be read or written is performed, and a rotation waiting operation of waiting until the target sector of the recording surface is positioned just below the head is performed. After these process, data reading or writing is executed. Therefore, to read the data at high speed, the time required for the seek operation and the rotation waiting operation must be shortened.
In the conventional data recording apparatus, in case of allocating a series of data items (e.g., video data, audio data, text data, still picture, program data, etc.), which are written in a continuous memory area. With this data allocation, when the plural different types of video data items in the data recording apparatus are simultaneously and sequentially read in a time division manner, the inner radial portion and the outer radial portion of the data recording apparatus are alternately accessed if some video data items are stored together in an inner radial portion of the data recording apparatus and other video data items are stored together in an outer radial portion thereof. Consequently, there is a problem that a situation where the distance for seeking target sectors continuously increases and therefore the entire time for the data access inevitably increases.
The above problems in the conventional art are summarized as follows. In the conventional apparatus, when a series of data items are allocated, these are written in a continuous area. Accordingly, when the plural different types of video data items in the data recording apparatus are simultaneously and sequentially read in a time division manner, there occurs a situation where the distance for seeking target sectors continuously increases and therefore the entire time for the data access inevitably increases if the video data items are separately stored in an inner radial portion of the data recording apparatus and in an outer radial portion thereof.